Transcription factors are critical regulators of gene expression. It is clear that these factors control the expression of many genes and, as such, mediate the biologic effects of agents such as "tumor promoters." The purpose of this project is to design mutants of transcription factors specifically aimed at inhibiting their biochemical and most importantly their biologic functions. The AP-1 complex has been specifically implicated in mediating the biologic effects of the tumor promoters "phorbol esters." A major component of this complex is the c-jun oncogene. We have created and tested a series of dominant-negative mutants of c-jun which are able to inhibit the biochemical functions of this oncogene. A transactivation mutant with a deletion of the N-terminal amino acids 2-122 has been shown to inhibit AP-1 transactivation and c-jun transformation. In addition, this mutant has been shown to inhibit cellular transformation by a wide range of oncogenes including c-fos, c-raf, ras, mos, and myc. Further, stable expression of this mutant protein in mouse epidermal cells can block phorbol ester induced tumor promotion. The mechanism of action of this mutant has been demonstrated to be heterodimerization with and neutralization of other AP-1 complex components such as c-fos. Our most recent efforts are aimed at furthering refining the potency and specificity of these mutants by creating smaller mutants with higher affinities for dimerization and DNA binding and testing them in specific human tumor systems such as breast and lung cancers. We have now created a series of c-jun mutants containing larger N-terminal deletions producing small peptides containing only the leucine zipper (dimerization domain). In addition, three DNA binding mutants including one with a point mutation at position 265, a deletion at positions 269-272, and one with an insertion of 3 amino acids at position 265 have been produced. All of these mutants have been demonstrated to have a dominant-negative phenotype. Future efforts are aimed at designing delivery mechanisms which might make these agents more clinically applicable. In vivo testing will be performed in model systems. Finally, we will expand these studies to include other transcription factors which play critical roles in human carcinogenesis such as CREB.